1. Field of the Invention
The present invention relates to an X-ray shielding mechanism to block off-axis X-rays in, for example, an X-ray cartridge of an X-ray analysis microscope.
2. Description of the Prior Art
FIG. 3 shows a basic structure of a fluorescent X-ray spectroscope which is an example of an X-ray analysis microscope using an X-ray cartridge 10. In FIG. 3, 2 represents an X-ray source, which has a filament 2a and a target 2b. The point at which electron current emitted from the filament 2a collides with the target 2b is an X-ray generating point P.
3a and 3b respectively represent X-ray guide tubes which are made of glass and are used to narrow X-rays Rx radiated from the X-ray generation point P and to irradiate a sample S with the X-rays Rx. As the X-ray guide tubes, two tubes having inside diameters of, for example, 10 xcexcm and 100 xcexcm are prepared. In the structure of this example, these X-ray guide tubes 3a and 3b are supported by a mount base 4. The mount base 4 slides in a direction horizontal (in the figure) to the X-ray source 2, whereby either one of the X-ray guide tubes 3a and 3b is selected and the sample S is irradiated with the X-rays Rx which are made to be in a properly narrowed condition.
Also, the above X-ray source 2 has an insertion portion 2c which is concaved therein for inserting the X-ray guide tubes so that the input ends of the X-ray guide tubes 3a and 3b can be brought closer to the X-ray generated point P, enabling more intense radiation of the X-rays Rx. In addition, the X-rays Rx applied to a portion other than an X-ray transmission window 2d are blocked so that the X-rays Rx are attempted to be applied to only the inside of either one of the X-ray guide tubes 3a and 3b. The X-rays Rx applied out of the inner peripheries of the X-ray guide tubes 3a and 3b are designed to be absorbed by the glass constituting the X-ray guide tubes 3a or 3b. 
The sample S is mounted on a sample stage 11 which can move in X-Y directions and the position of the sample S can be controlled by a computer 12 through a stage control circuit 11a. The spectroscope is also provided with a detector 13 for detecting various fluorescent X-rays Rf generated from the sample S and provides a signal to a process circuit 14 which outputs the detected X-rays Rf as, for example, a fluorescent X-ray spectrum to the computer 12. Namely, in this structure, the control of the stage 11 in the direction of X-Y axes is made by the computer 12 to enable the reproduction of the mapping image of element distribution in a sample by using fluorescent X-ray spectroscopy.
However, in order to block the X-rays Rx by using the X-ray guide tubes 3a and 3b, the entire length of the X-ray guide tubes 3a and 3b must be used. Also, since in the X-ray cartridge 10 having the above structure, only the X-ray transmission window 2d is formed on the side of the end from which the X-rays Rx are introduced and the X-rays Rx applied to the other portion are blocked, there is a possibility that the X-rays Rx applied at a relatively large divergent angle xcex1 pass through the outer surface of the X-ray guide tubes 3a and 3b and are eventually applied to the sample S. Specifically, there is a possibility that fluorescent X-rays Rfxe2x80x2 generated by leaking X-rays Rxxe2x80x2 appear as a noise.
In order not to allow such a problem to arise, as shown by the enlarged sectional view, a material like a solder cream H is applied to a space formed between each of the X-ray guide tubes 3a and 3b and a shielding portion of the mount base 4 and is soldered by heating to prevent the sample S from being irradiated with the X-rays Rxxe2x80x2 which have penetrated the X-ray guide tubes 3a and 3b. This, in turn, gives rise to the problem that laborious works of, for instance, applying the solder cream H are required, thereby increasing the cost to make the X-ray cartridge 10.
On the other hand, it is considered that a shielding plate is disposed on the side of the end from which the X-rays Rx are emitted. However, it is of importance to bring the X-ray guide tubes 3a and 3b close to the sample S in order to prevent the focus from being blurred. Disposing a shielding plate between the X-ray guide tubes 3a and 3b and the sample S can cause the guide tubes to be distant from the sample S and is hence undesirable. Also, there is a possibility that an observation field by visual observation and a monitor would be blocked by the shielding plate disposed on the side of the end from which the X-rays Rx are emitted.
The present invention has been provided taking the above situation into consideration and has an object of providing an X-ray shielding mechanism which can block leaking X-rays other than the X-rays collected by an X-ray guide tube.
The above object is attained by an X-ray shielding mechanism being provided with an X-ray cartridge comprising an X-ray source which radiates X-rays and a glass X-ray guide tube with an inner peripheral surface into which the X-rays are introduced, the cartridge further comprising a metallic protective pipe which is disposed outside of the X-ray guide tube whereby the X-rays which are transmitted from the side surface of the X-ray guide tube can be blocked.
Accordingly, it is possible to allow the X-rays to be reflected by the inner peripheral surface of the X-ray guide tube and to be narrowed so that the X-rays have a proper radiation area. Also, the X-rays transmitted from the side surface of the X-ray guide tube can be blocked. It is therefore possible to completely limit the area irradiated with the X-rays. As a consequence, the use of this leaking X-ray shielding mechanism enables it possible to eliminate an adverse effect produced by the leak X-rays to carry out an analysis with high accuracy.
A leaking X-ray shielding mechanism according to a second aspect of the present invention is provided with an X-ray cartridge comprising an X-ray source which radiates X-rays and a glass X-ray guide tube with an inner peripheral surface into which the X-rays are introduced, the cartridge further comprising an X-ray shielding plate which is made of a metal, has a window for introducing X-rays into the X-ray guide tube and is disposed on the side of the input end of the X-ray guide tube and a metallic protective pipe which has a predetermined length extending from the side of the input end at a predetermined distance from the X-ray source to the side of the end, from which the X-rays are emitted, and which is disposed outside of the X-ray guide tube whereby the X-rays which pass through the entrance window and is transmitted from the side surface of the X-ray guide tube can be blocked.
According to the above leak X-ray shielding mechanism, only X-rays passing through the X-ray guide tube can be applied to a sample and hence the area irradiated with X-rays can be surely decreased that much more. Accordingly, measurement errors caused by leaking X-rays can be prevented.
When the relation, r1/x1 less than r2/x2, is established between the diameter r1 of the entrance window of the X-ray shielding plate, the distance x1 from the X-ray generating point of the X-ray source to the X-ray shielding plate, the distance x2 from the X-ray generating point to the input end of the protective pipe and the inside diameter of r2 of the protective pipe, leaking X-rays can be blocked only the use of X-ray shielding in the most limited range, which reduces the production cost that much more.
When the X-ray cartridge has a plurality of X-ray guide tubes and a mount base which supports these X-ray guide tubes and switches the X-ray guide tubes to each other, making it possible to use the changed X-ray guide, the intensity and thinness of the X-rays to be applied can be changed.
When the mount base supports the metallic X-ray shielding pipe positioned outside of the X-ray guide tube and the X-ray shielding plate positioned on the side of the input end of the X-ray guide tube is supported by the X-ray shielding pipe, the X-ray shielding plate can be surely supported at a fixed position with regard to the X-ray guide tube.